Composite charge for metallurgical processing

ABSTRACT

A composite charge for metallurgical processing which reduces the content of non-metallic inclusions in the end product(s) comprises 40-83 wt. % of a metallic agent, 17-50 wt. % of an oxide agent and 0.1-10.0 wt. % of a carbonaceous agent. The carbonaceous agent includes a mixture of metal carbides and free carbon, preferably graphite, having a ratio in the range of 0.1-10.0:1.

FIELD OF THE INVENTION

The present invention relates in general to ferrous metallurgy, and moreparticularly to a composite charge used for the production of steel andalloys.

BACKGROUND OF THE INVENTION

It is known that a composite charge can be produced from alloyed steelscrap and/or alloy scrap. The charge generally includes a metallicagent, an oxidizing agent and a reducing agent. In order to reduce theloss of alloying elements (due to melting), increase the yield of theend product, and lower the production costs, such a charge generallycontains shavings of alloyed steel or alloy as the metallic agent, scaleof a basic alloy and/or a mixture of oxides as the oxidizing agent, andscreenings of aluminum shavings and/or aluminum "middlings" (i.e.,products of medium quality, grade and/or size) as the reducing agent.

The composite charge generally contains: 15-50 wt. % shavings of alloyedsteel or alloy; 35-55 wt. % scale of basic alloy and/or a mixture ofoxides; and 17-30 wt. % screenings of aluminum shavings and/or aluminummiddlings.

A major drawback of this charge material is the relatively low yield ofusable product. This is due, in significant part, to the inherentdifficulties associated with mixing charge components that differsignificantly in physical and chemical properties, especially density.Other factors which contribute to the low yield include the inherentproblems associated with conventional mechanical mixing methods (e.g.,equipment performance, mix indices) and the large difference in thegranulometric, physical and chemical properties of the constituentcomponents, which may not allow the production of a well developedsurface on the reactants, especially under conditions where the chargehas a relatively large mass. Surface irregularities on the reactanceadversely effect the process kinetics, slow the reduction of oxides,lower the percent extraction of elements from the oxides and increaseconsumption of the reducing agent to levels commensurate with the amountof metal additive in the charge.

Further, because it is virtually impossible to use a charge of knowncomposition during melting of steel (with oxidation), the applicabilityof such a charge material is limited to re-melting processes and to theproduction of steels of one brand assortment.

Additional problems associated with the conventional charge materialinclude (i) aluminum in the form of screenings of aluminum shavingsand/or aluminum middlings is a costly component and in very shortsupply, and (ii) dispersion of non-metallic inclusions of oxides andaluminum nitrides tend to contaminate and, hence, adversely effect thequality of the end product.

Finally, the elevated reducing agent content in the charge and its highconsumption further increases the costs associated with this chargematerial and lowers the technical and economic indices of its use.

It is therefore an object of the present invention to provide acomposite charge for metallurgical processing which increases the yieldof usable product.

It is another object of the invention to provide a composite charge formetallurgical processing that lowers the production costs of the chargematerial and the products made therefrom.

It is yet another object of the invention to provide a composite chargefor metallurgical processing which reduces the content of non-metallicinclusions in the products made therefrom.

SUMMARY OF THE INVENTION

The composite charge of this invention comprises 40-83 wt. % of ametallic agent, 17-50 wt. % of an oxide agent and 0.1-10 wt. % of acarbonaceous agent. The metallic agent preferably includes acarbide-forming component comprising a material selected from the groupconsisting of iron, chromium, manganese, boron, calcium, vanadium,tungsten and mixtures thereof. The carbonaceous agent comprises amixture of metal carbides and free carbon, preferably graphite, having aratio in the range of 0.1-10.0:1. The oxide agent may comprise oxidizedflux bearing and flux free iron-ore materials, i.e. , agglomerate orpellets of raw ore and their waste products, scale, oxidized metalscrap, fragmentized metal waste, and solid oxidizers obtained byagglomeration of the dust and sludge from metallurgical processes.

DESCRIPTION OF PREFERRED EMBODIMENTS

The composite charge material of the present invention substantiallyreduces or eliminates the disadvantages and shortcomings associated withprior art charge materials. According to the invention, the compositecharge material comprises 40-83 wt. % of a metallic agent, 17-50 wt. %of an oxide agent and 0.1-10 wt. % of a carbonaceous agent. In apreferred embodiment of the invention, the composite charge comprises40-82.8 wt. % of a metallic agent, 17.1-50 wt. % of an oxide agent and0.1-10 wt. % of a carbonaceous agent.

According to the invention, the metallic agent (i.e., metal containingmaterial) includes a carbide forming component comprising a materialselected from the group consisting of iron, chromium, manganese, boron,calcium, vanadium, tungsten and mixtures thereof. Thus, conventionaliron-carbon alloys, such as basic pig iron, may be employed as themetallic agent.

The oxide agent (i.e., oxide containing material) may comprise oxidizedflux bearing and flux free iron-ore materials, i.e. , agglomerate orpellets of raw ores and their waste products, scale, oxidized metalscrap, fragmentized metal waste and solid oxidizers obtained byagglomeration of flue dust and sludge from metallurgical processes. Thecomposition of various exemplary oxide agents is set forth in co-pendingapplication Ser. No. 08/567,550, Filed Dec. 5, 1995, incorporated byreference herein.

In a preferred embodiment of the invention, the oxide agent comprises5-50 wt. % of a slag forming component. As will be recognized by onehaving ordinary skill in the art, the slag forming components mayinclude lime stones, sinter, fire clay and the like.

A key characteristic of the invention is that the charge materialincludes a carbonaceous agent (i.e., carbon containing material) as areducing agent. According to the invention, the carbonaceous agentcomprises a mixture of metal carbides and free carbon, preferably in theform of graphite. In a preferred embodiment, the metal carbides and freecarbon have a ratio in the range of 0.1-10.0:1.

According to the invention, the production of the composite charge isaccomplished by virtue of the fact that the charge comprises a mixtureof components in monolithic pieces that are capable of predominantlyendothermic reactions. As the charge is heated, the oxides contained inthe charge are reduced by the carbonaceous (reducing) agent. As aresult, the oxides are thus reduced to the metallic state, the gaseousreaction products are driven into the slag, and the excess carbon isoxidized by the oxide agent.

The energy produced as a result of exothermic reactions occurringbetween the oxygen of the oxidizing agent and the elements of thereducing agent that are present in the metallic agent (having, a higheraffinity for oxygen than carbon, e.g., Si, Mn) is an additional sourceof heat.

As stated above, according to the invention, the source for supply ofthe reducing agent (in the form of carbon) is the carbonaceous agent. Anadditional source is the carbon dissolved in the metallic agent in theform of metal carbides and/or free carbon.

The oxides in the oxide agent and, in part, in the slag-formingcomponents are the source of oxygen (the oxygen carrier). According tothe invention, as the charge is heated and melted, oxygen is exchangedbetween the oxide agent and the reducing agent. As a result, the carbonis oxidized to carbon monoxide, the latter being evolved in the form ofa gaseous phase that agitates the melt, and the metal oxides, giving upoxygen, are reduced to the metallic state. The composition of the chargecan thus be tailored to ensure the highest possible reduction of theoxides and the production of steel and/or alloy having the requisiteconcentration of carbon.

Significant improvements in the technical and economic indices arerealized by tailoring the composition of the charge and employing it in"lumped" form, where the charge components (or elements) exhibit ahighly developed phase contact surface. According to the invention, thephase contact surface is formed and/or developed by pouring the metallicagent onto the melt during processing, the amount of which being heldconstant during loading of the charge into the furnace, heating, andcalcination. This improves the kinetics of the oxidation-reductionreaction(s), and increases the process rate and percent extraction ofelements from the metal oxides (the yield of usable product).

Applicants have found that where an iron-carbon melt is the metallicagent and iron oxides are the oxide agent, the proposed charge has acarbon oxidation rate in the range of 0.4-0.8% C/min, i.e., at the levelof the oxygen-converter process. Here, the redox reaction proceeds at areduced temperature, beginning at 800-850° C., and has a high rate. Forthis reason, nearly complete reduction of the oxides and maximum removalof carbon are attained.

Replacing the aluminum, which in the prior art material simultaneouslyacts as reducing agent and heat source, with an inexpensive reducingagent, such as carbon, and supplying heat to compensate for the energyconsumption resulting from the endothermic reactions of the reduction ofthe oxides by carbon, makes it possible to sharply reduce the cost ofthe charge and, hence, the end product. As will be recognized by onehaving ordinary skill in the art, the cost per unit heat in the form ofelectric power is always lower than the cost of heat released by theoxidation of aluminum.

Further, the quality of the end product (metal) is improved since thegaseous reaction products resulting from the oxidation of carbon by theoxygen (i) agitate the melt of the composite charge and the entire metalbath, driving the gases out of the melt, (ii) promote the migration ofnonmetallic inclusions to the slag, and (iii) prevent the gases from thefurnace atmosphere from penetrating into the metal bath.

The agitation of the metal bath by the carbon monoxide bubbles alsointensifies the heat transfer therein, facilitating a lower energyconsumption. Further, the presence of carbon monoxide in the workingvolume of the furnace and in the charge layer lowers the free oxygencontent in the furnace atmosphere and the percent oxidation of the solidcharge and liquid metal. As a result, there is an additional increase inmetal extraction and in the yield of usable product.

After the charge melts, the metal comprises an alloy of elements reducedfrom the oxides and metallic agents fused by heat from the externalsource. The composition of the slag remains practically unchanged sincegaseous oxides of carbon and not liquid oxides are the reaction product.A small fraction of the oxide component does however migrate to theslag. This makes it possible to adjust the quantitative composition ofthe slag phase according to process requirements, particularly bypre-injecting the slag-forming components into the starting compositecharge or, as melt-down of the charge proceeds, directly into thefurnace.

The use of elements of the metallic agent, such as carbonaceous silicon(introduced as metallic Si or SiC) and/or a mixture of metal carbidesmakes it possible to increase the utilization of the carbon and tosignificantly increase the stability of the carbonization process. Thisis due to the fact that silicon, which under the noted conditions has ahigher affinity for oxygen than carbon, oxidizes first.

The introduction of slag-forming agents, such as lime, enhances thethermodynamic process of silicon oxidation, since the SiO₂ formed isbound in thermodynamically stable calcium silicates. Consequently, byreadily oxidizing, the silicon inhibits carbon oxidation, promoting amore complete and stable uptake of the carbon by the metal bath.

The composite charge of the invention also improves the conditions formelt-down of the charge and, thus, refining of the metal. In particular,the carbon content may be controlled and, thus, selected to lower themelting point and the silicon content may also be controlled andselected to increase the melting point. Further, oxidation of the carbonpromotes mixing of the melt, thereby increasing the stability andefficiency of the arcs.

Referring to Table 3 there is shown the test results (i.e., technicaland economic indices) of end products employing various compositions ofcomposite charge materials according to the invention.

The technical compositions of the charge materials investigated byApplicants are set forth in Tables 1 and 2. As illustrated in Table 2,iron-carbon alloys containing various amounts of carbon were employed asthe metallic agent. The following agglomerate and iron-ore pellets wereemployed as the oxide agent:

    ______________________________________                                                      Pellets of Mikh.                                                                          Pellets of Lebedinskii                              Agglomerate   GOK         GOK                                                 ______________________________________                                        Fe total                                                                            56.83       62.70       66.50                                           FeO   12.35       1.59        1.11                                            Fe.sub.2 O.sub.3                                                                    67.50       87.90       93.07                                           SiO.sub.2                                                                           7.20        7.36        4.60                                            Al.sub.2 O.sub.3                                                                    1.65        0.21        0.30                                            CaO   8.32        2.37        0.17                                            MgO   1.46        0.24        0.25                                            MnO   0.48        0.010       0.02                                            TiO.sub.2                                                                           0.13        0.02        0.035                                           P.sub.2 O.sub.5                                                                     0.11        P = 0.022   0.011                                           S     0.040       0.01        0.036                                           ______________________________________                                    

In addition to carbon, iron carbide containing 95% Fe₃ C, 2% Fe₃ O₄, 2%SiO₂, 0.05% Al₂ O₃, and 0.95% total CaO+MgO, and free carbon (in theform of graphite) were employed as the carbonaceous agent.

                                      TABLE 1                                     __________________________________________________________________________           Chemical composition of composite charge                                                             Carbonaceous                                    Item No.                                                                             Metallic Agent                                                                       wt. %                                                                             Oxide Agent                                                                           wt. %                                                                             Agent   wt. %                                   __________________________________________________________________________    1-the prior art                                                                      Shavings of                                                                          28  Scale of basic                                                                        46  Reducing agent                                                                        26                                             alloyed steel                                                                            alloy                                                       screenings of                                                                                               aluminum                                                                      shavings                                        2      Basic pig iron                                                                       40  Agglomerate                                                                           50  Iron carbide                                                                          10                                      3      Chrome-nickel                                                                          82.8                                                                            Iron-ore pellets                                                                        17.1                                                                            Iron carbide                                                                            0.1                                          pig, brand from Mikh.                                                         LKhCh4     GOK                                                         4      Basic coke pig                                                                       70  Iron-ore pellets                                                                      25  Iron carbide 10                                                                       5                                              iron, brand                                                                              from Mikh.  parts, graphite 1                                      PVK 1      GOK         part                                            5      Cast iron from                                                                       60  Iron-ore pellets                                                                      30  Carbide Fe.sub.3 C,                                                                    5+                                            Chusovskii from Leb. GOK                                                                             graphite                                                                              5                                              Metallurgical                                                                 Plant                                                                  __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________    Chemical Composition of Composite Charge as a Function of Proportions of      Its Components                                                                Item                                                                             Content, wt. %                                                             No.                                                                              C  Fe met                                                                            FeO                                                                              Fe.sub.2 O.sub.3                                                                  SiO.sub.2                                                                        Al.sub.2 O.sub.3                                                                  CaO                                                                              MgO                                                                              MnO                                                                              TiO.sub.2                                                                        P  S  Si Mn Cr V  Ti Ni Total             __________________________________________________________________________    2  2.38                                                                             46.48                                                                             6.24                                                                             33.89                                                                             3.90                                                                             0.88                                                                              4.3                                                                              0.84                                                                             0.25                                                                             0.07                                                                             0.07                                                                             0.04                                                                             0.26                                                                             0.20                                                                             0.1                                                                              -- -- 0.01                                                                             99.97             3  2.99                                                                             74.61                                                                             0.27                                                                             15.03                                                                             1.26                                                                             0.04                                                                              0.41                                                                             0.04                                                                             0.002                                                                            0.003                                                                            0.004                                                                            0.002                                                                            1.27                                                                             0.75                                                                             2.03                                                                             -- -- 0.93                                                                          99.8                 4  3.6                                                                              69.49                                                                             0.43                                                                             22.04                                                                             1.93                                                                             0.06                                                                              0.61                                                                             0.08                                                                             0.003                                                                            0.005                                                                            0.01                                                                             0.01                                                                             1.06                                                                             0.6                                                                              -- -- -- --  99.95            5  7.93                                                                             60.36                                                                             0.36                                                                             28.20                                                                             1.39                                                                             0.1 0.08                                                                             0.1                                                                              0.006                                                                            0.011                                                                            0.05                                                                             0.03                                                                             0.35                                                                             0.15                                                                             0.33                                                                             0.33                                                                             0.13                                                                             --  99.86            __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________    Technical and Economic Indices                                                              Decrease in                                                                   production                                                                          Content of                                                                          Oxygen                                              No. of        cost of                                                                             nonmetallic                                                                         content in                                          charging stock                                                                       Yield of                                                                             charging                                                                            inclusions in                                                                       metal before                                                                        N.sub.2 content in                                                                  Assortment of                           composition                                                                          usable product                                                                       stocks, %                                                                           metal, points                                                                       deoxidizing                                                                         metal, %                                                                            metals Remarks                          __________________________________________________________________________    Prior art-1                                                                          90-91.5                                                                              200   No data                                                                             No data                                                                             No data                                                                             One brand:                                                                           Production                                                             12Kh18N10T                                                                           cost  for this                                                                item! was                                                                     taken as 100%                                                                 of production                                                                 cost.                            2      92     100   4.5   0.22  0.025 St. 10-20                               3      93     120   3.5   0.2   0.020 St. 10-20 and                                                                 low-alloy steel                         4      98     110   3.0   0.13  0.018 St. 10-20                               5      93     115   2.5   0.10  0.15  St. 10-20 and                                                                 low-alloy steel                         __________________________________________________________________________

It was found that when the content of metallic agent in the charge isless than 40%, and the content of oxide agent and carbonaceous agent aremore than 50% and 10%, respectively, the yield (percentage extraction)of metal is reduced by virtue of the ejections and entrainment of solidparticles due to the turbulent oxidation process of the carbon. If thecontent of the metallic agent in the charge is more than 82.8% and thecontent of oxide agent and carbonaceous agent is less than 17.1% and0.1%, respectively, there is an increased amount of carbon in the alloyand impurities of nonferrous metals.

As illustrated in Table 3, excellent results with respect to all keyindices were obtained with the following charge composition: metallicagent 40-82.8 wt. %, oxide agent 17.1-50 wt. %, and carbonaceous agent0.1-10 wt. %.

The best results were obtained by using a charge with the followingcomposition: metallic agent 70 wt. %, oxide agent 25 wt. %, andcarbonaceous agent 5 wt. %. This composition is optimal with respect toall key engineering and economic parameters.

While preferred embodiments and their technical advantages have beendescribed in the above detailed description, the present invention isnot limited thereto but only by the core and spirit of the appendedclaims.

What is claimed is:
 1. A composite charge for metallurgical processing,comprising:40-83 wt. % of a metallic agent comprising an iron-carbonalloy; 17-50 wt. % of an oxide agent; and 0.1-10 wt. % of a carbonaceousagent comprising a mixture of metal carbides and free carbon.
 2. Thecomposite charge of claim 1, wherein said composite charge comprises40-82.8 wt. % of said metallic agent.
 3. The composite charge of claim1, wherein said composite charge comprises 17.1-50 wt. % of said oxideagent.
 4. The composite charge of claim 1, wherein said metallic agentincludes a carbide forming component.
 5. The composite charge of claim4, wherein said carbide forming component comprises a material selectedfrom the group consisting of iron, chromium, manganese, boron, calcium,vanadium, tungsten and mixtures thereof.
 6. The composite charge ofclaim 1, wherein said carbonaceous agent comprises a mixture of metalcarbides and free carbon, the ratio of metal carbides to free carbonbeing in the range of 0.1-10.0:1.
 7. The composite charge of claim 6,wherein said free carbon comprises graphite.
 8. The composite charge ofclaim 1, wherein said oxide agent comprises 5-50 wt. % of a slag formingcomponent.
 9. The composite charge of claim 1, wherein said oxide agentcomprises iron ore, slag, flue dust, sludge from metallurgicalprocesses, and mixtures thereof.
 10. The composite charge of claim 1,wherein said metallic agent comprises pig iron.
 11. The composite chargeof claim 1, wherein said composite charge is prepared by addition of themetallic agent in molten form to the oxide agent and the carbonaceousagent.
 12. The composite charge of claim 6, wherein said compositecharge is prepared by addition of the metallic agent in molten form tothe oxide agent and the carbonaceous agent.
 13. The composite charge ofclaim 8, wherein said composite charge is prepared by addition of themetallic agent in molten form to the oxide agent and the carbonaceousagent.